Centrosymmetric Structure Research Articles

Second Harmonic Generation in the Polar A′SmNb2O7 (A′ = Rb, Cs) Dion–Jacobson Layered Perovskites

Members belonging to the Dion–Jacobson (DJ) family of layered perovskites have time and again proven to be the preferred materials of choice for the exploration and identification of polar structures. We report two noncentrosymmetric n = 2 DJ members, A′SmNb2O7 (A′ = Rb, Cs), prepared by high-temperature solid-state reactions, thus expanding the polar n = 2, DJ series as A′ANb2O7 (A′ = Rb, Cs; A = La, Pr, Nd, Sm, Bi). Optical second harmonic generation measurements utilizing 1064 nm substantiated the existence of Type I phase matchable compounds, and the efficiencies were 4 to 6 times higher than the standard KDP. Structural refinements by the Rietveld method confirm the polar orthorhombic space groups of I2cm and P21am, respectively, for RbSmNb2O7 [a = 5.4368(3) Å, b = 5.3944(3) Å, c = 21.9051(1) Å] and CsSmNb2O7 [a = 5.4669(5) Å, b = 5.4158(4) Å, c = 11.1437(1) Å]. The orthorhombic distortions and symmetry lowering were further supported by the Raman spectroscopy measurements. The difference in the orthorhombic a and b parameters (∼0.05 Å) possibly originates from the chemical pressure induced by the smaller ionic size of Sm3+ (1.24 Å, XII) as compared to other Ln3+ (La, Pr, Nd) ions. Ferroelectric switching of A′SmNb2O7 (A′ = Rb, Cs) oxides is demonstrated by the polarization hysteresis loops observed at room temperature with remanent polarization values of 5.3 and 2.0 μC/cm2 corresponding to the Rb and Cs analogues. Variable-temperature powder X-ray diffraction measurements confirmed the phase transition from polar to anti-polar transitions around temperatures ∼1273 and ∼1173 K, respectively, for the Rb and Cs analogues. Structural analysis results in the identification of prototype tetragonal (a ∼ 3.88 Å, c ∼ 11.20 Å) centrosymmetric structures relating the transition temperatures to potential Curie temperatures. The transitions coincide with the observed Curie point of 1113 K for CsSmNb2O7, from the temperature-dependent relative permittivity measurements, and a much higher temperature is expected for the Rb analogue.

Synthesis, luminescence and magnetic properties of dinuclear complexes based on a “pincer” Schiff base and different β-diketonate ligands

Twelve new dinuclear rare earth complexes in three series were successfully synthesized with a “pincer” Schiff base H2L and different β-diketonate ligands: Ln2(acac)2(L)2·2C2H5OH (Ln = Eu (1), Tb (2), Dy (3), Er (4)), Ln2(dbm)2(L)2·2C3H7NO (Ln = Eu (5), Tb (6), Dy (7), Er (8), Yb (9)), Ln2(TTA)2(L)2·2H2O (Ln = Eu (10), Tb (11), Dy(12)). (H2L = 3-aminopyrazine-2-carboxylic acid [(2-hydroxybenzylidene)] hydrazide; Hacac = acetylacetone; Hdbm = dibenzoylmethane; HTTA = 2-thiophene trifluoroacetone). These complexes are centrosymmetric dinuclear structures and RE3+ ions are bridged by oxygen atoms in carbonyl of Schiff base to form the core unit of Ln2O2. The characteristic emission peaks of Er3+ and Yb3+ in 4, 8 and 9 can be observed in Near-infrared luminescence spectra, that is confirmed the central ions were sensitized effectively via ligands. Moreover, 1, 5, 6 and 10 were sensitized in various degrees. The dynamic magnetization curves indicate that 3, 7 and 12 are typical SMMs with slow magnetic relaxation behaviors. Their effective energy barriers are 48.20 K (3) and 42.30 K (12) under 3000 Oe dc field and 81.89 K (7) under zero dc field. The pre-exponential factors (τ0) are 1.35 × 10−6 s (3), 1.38 × 10−10 s (7) and 4.93 × 10−6 s (12), respectively. It is confirmed that the magnetic properties of SMMs can be regulated by different β-diketonate ligands.

Polarized neutron scattering study of the centrosymmetric skyrmion host material Gd2PdSi3

We investigated magnetic structures of the centrosymmetric skyrmion material ${\mathrm{Gd}}_{2}{\mathrm{PdSi}}_{3}$ by means of polarized neutron scattering near zero field with an isotope-$^{160}\mathrm{Gd}$-enriched single crystal. In a previous study, magnetic structures in ${\mathrm{Gd}}_{2}{\mathrm{PdSi}}_{3}$ at low temperatures were studied by resonant x-ray scattering measurements [T. Kurumaji et al., Science 365, 914 (2019)]. The present polarized neutron results confirm that the magnetic structure in zero field has elliptic screw-type magnetic modulation with a propagation vector of $(q,0,0)$ with $q\ensuremath{\sim}0.14$ and its equivalents. As the temperature increases, the system undergoes a magnetic phase transition while keeping the incommensurate $q$-vector of $(q,0,0)$. We found that the thermally induced phase has sinusoidal magnetic modulations with magnetic moments perpendicular both to the $c$ axis and to the $\mathbit{q}$-vector. We also investigate the spin-helicity degree of freedom in the ground state by polarized neutrons, revealing that the system contains equal fractions of the left-handed and right-handed screw-type orders as expected from the centrosymmetric crystal structure.

New Cu(II), Mn(II) and Mn(III) Schiff base complexes cause noncovalent interactions: X-ray crystallography survey, Hirshfeld surface analysis and molecular simulation investigation against SARS-CoV-2

In this study, polynuclear Cu(II) complex (1), Mn(II) and Mn(III) complex (2) have been prepared with a Schiff base ligand derived from 2-Hydroxy-3-methoxybenzaldehyde with 2-amino-2-methyl-1-propanol. The compounds were characterized by elemental analysis, FT-IR, and UV–Vis spectroscopy. The molecular and crystal structures of (1–2) were determined by the single-crystal x-ray diffraction technique. It turned out that Cu(II) complex (1) forms an S4-symmetrical tetrameric cage structure, with square-planar coordinated Cu and bridging O atoms at the vertexes of the approximate cube. In the crystal structure of 1, there are large channels along the c-axis, between the tetramers; the solvent– DMSO molecules, occupies these channels. In turn, the complex (2) creates a centrosymmetric trimeric structure, with three octahedrally coordinated Mn ions bridged by O atoms from ligand molecules and acetate ions. The electrochemical behavior studies of the complexes in DMSO displayed the electronic effects of the groups on the redox potential. The redox behavior of Schiff base (1) and (2) complexes included quasi -reversible and irreversible voltammograms, respectively. Intermolecular interactions in the solid states were studied by Hirshfeld surface analysis. These studies provide a comprehensive description of these inter-contact exchanges using an attractive graphical representation using Hirshfeld surfaces and fingerprint plots, along with enrichment ratios. Furthermore, assessment of the inhibitory effect against coronavirus (main protease SARS-CoV-2) was performed by a molecular docking study for both complexes (1 and 2). Both complexes showed a good affinity for CoV-2 for PDB protein ID: 6M03 and 6Y2F.

The effect of light-irradiated area on the spin dependent photocurrent in zigzag graphene nanoribbon junctions.

In this work, we study the photogalvanic effect of a zigzag graphene nanoribbon junction with a centro-symmetrical structure which consists of 8 zigzag chains by density functional calculations. Specifically, we focus on the cases where the irradiated region is just part of the central region and located at different positions, with an aim to see how the spin dependent photocurrents will change and whether pure spin current can be obtained. It is found that the magnitude of the spin-dependent photocurrents increases with a gradual increase of the irradiated region and pure spin current is achieved when and only when the entire central region is irradiated. In addition, we studied the additive effect in this device to see that if we divide the central region into two parts, whether the sum of the spin current generated by irradiating the two parts individually is equal to that produced when the entire central region is irradiated. It is found that the sum of the spin currents produced by irradiating the two parts individually is smaller than that obtained by irradiating the whole central region, which means that the rule of "1 + 2 = 3" does not hold and the coupling effect between the two parts is important in photocurrent generation.

Cd(II) Dithiocarbamate Complexes: Synthesis, Spectral Studies, Thermogravimetric Analysis and Semiconducting Behaviour

Five new homoleptic Cd(II) dithiocarbamate complexes (1-5) have been synthesized and characterized by IR, NMR, UV-visible spectroscopic techniques along with thermogravimetric analysis. Singlecrystal X-ray diffraction study of complex 1 revealed a triclinic system with space group P1 and possesses a centrosymmetric dimeric structure. In this complex, both C–H···S and C–H···π intermolecular interactions are playing a crucial role in the stabilization of the dithiocarbamate complex. Complexes (1-5) show weak conductivity at ambient temperature (σrt = 10-9-10-10 S·cm-1) because of the absence of M···S/S···S intermolecular stacking. Plot of log σ versus T–1 in the 303-363 K range indicates their semiconducting behaviour. However, their electrical conductivities gradually increase with increasing temperature and ideally decrease with decreasing temperature range showing their semiconducting nature. TGA showed thermal decomposition of complexes into CdS as the final product with grain size of 1-10 nm.

Electroactive properties and piezo-tribo hybrid energy harvesting performances of PVDF-AlFeO3 composites: role of crystal symmetry and agglomeration of fillers.

Inorganic filler-loaded PVDF-based composites have been very widely used for electrical and energy harvesting applications in recent times. In this regard, the effects of different parameters of fillers like size, shape, chemical states, distribution, functional properties, and many others on the output performance of PVDF have been widely studied. However, the effect of another important parameter, namely the crystal symmetry of the filler, in tuning the energy harvesting performance of PVDF has been rarely explored. Therefore, to explore this fact, here we develop PVDF-based composite films by using two types of AlFeO3 fillers, one with rhombohedral R3̄c symmetry (AFRH) and another with an orthorhombic Pc21n structure. Ferrite-based oxides have been chosen here as fillers due to their good dielectric compatibility with PVDF. On the other hand, AlFeO3 has been chosen due to the simplicity of synthesizing it with both centrosymmetric and non-centrosymmetric crystal structures and the scarcity of reports exploring the energy-harvesting performance of AlFeO3-based polymer composites. A significant difference in particle agglomeration has also been observed here between the mentioned two types of AlFeO3 fillers which was mainly due to their specific synthesis conditions. The electroactive properties of PVDF have been observed to be mostly dependent on filler agglomeration. However, the crystal symmetry has shown a strong effect on the piezoelectric energy harvesting performances. As a result of these facts, the piezo-tribo hybrid energy harvesting performance, which depends on both the dielectric permittivity and piezoelectric activity, has been observed to be better for the AFRH5-based hybrid device (AFRH5H) (with ∼72 V open circuit voltage and ∼45 μW cm-2 power density) compared to that of the AFOR5-based hybrid device (AFOR5H). The real-life applications of all the energy harvesting devices have also been demonstrated here.

Efficient detection of Al3+ and B4O72− over trigonal prism In(iii) complex

A novel mononuclear trigonal prism indium(iii) complex, namely, In(H2nha)3 (1) (H3nha = 3-hydroxy-2-napthanoic hydroxamic acid), displaying efficient detection of Al3+ and B4O72− by fluorescence enhancement effect.

Probing the antiferromagnetic structure of bilayer CrI3 by second harmonic generation: A first-principles study

Two-dimensional antiferromagnetic materials with robust second harmonic generation (SHG) have been attracting significant research interest. In recent experiments, enhanced SHG from layered antiferromagnet (AFM) bilayer chromium trioxide $({\mathrm{CrI}}_{3})$ with $A$-type antiferromagnetic order has been observed. However, bilayer ${\mathrm{CrI}}_{3}$ with $A$-type, $C$-type, and $G$-type antiferromagnetic order may simultaneously occur in experimental synthesis, as the total free-energy difference between the three AFMs is small. Here, based on symmetry analysis and first-principles calculations, we study the three kinds of bilayer AFMs with and without the spin-orbit coupling (SOC) effect. We find that for all three types, the $i$-type SHG response vanishes due to the centrosymmetric lattice structure. However, significant $c$-type SHG response can arise in $A$-type and $C$-type AFMs but still vanishes for $G$-type AFM. Under normal incidence, both $A$-type and $C$-type AFMs exhibit three independent nonvanishing SHG components. Remarkably, the nonvanishing SHG components of $A$-type and $C$-type AFMs are mutually exclusive, namely, the SHG components that are finite for $A$-type vanish for $C$-type and vice versa. In particular, the SHG of both $A$-type and $C$-type AFMs is sensitive to the SOC effect and it becomes enhanced when the SOC effect is fully considered. Hence, the SHG response would be an efficient method for probing bilayer ${\mathrm{CrI}}_{3}$ with different antiferromagnetic orders.

Novel phenoxo-bridged di- and tri-nuclear Cu(II) salamo-like complexes driven by various counter-anions

A N2O3-donor aldehyde-appended salamo-like ligand H2L has been designed and synthesized successfully, and can be used to prepare [{Cu(L)}2] (1) and [Cu3(L)2(EtOH)2]·2ClO4 (2) with different nuclearity and extraordinary structures by changing the reaction conditions (various counter-anions and solvent molecules). In addition, the structures of two complexes were determined by single-crystal X-ray diffraction experiments. The results showed that complex 1 is a novel (L)2−: Cu(II) = 1:1 non-centrosymmetrical homobinuclear dimeric Cu(II) complex, where Cu1 sited in the N2O2-donor position also coordinates with one phenolic oxygen atom of another ligand (L)2− moiety to construct two discrete metal–ligand [Cu(L)] units. However, Noteworthy, the influence of the interaction of multiple counter-anions and solvents led to the formation of a novel (L)2−: Cu(II) = 2:3 homotrinuclear centrosymmetric sandwich-like dimeric structure in complex 2, where Cu2 located at the O6 position bridges two [Cu(L)(EtOH)] metalated ligand moieties. Finally, two novel homopolynuclear dimeric Cu(II) complexes were characterized by elemental analysis, coordination cavities analyses, infrared spectroscopy (IR), electrostatic potential analyses (ESP), interaction region indicator (IRI) analyses and DFT calculation, UV–vis, luminescence spectroscopy and Free regions analyses.

Antiferroelectric-like Behavior in a Lead-Free Perovskite Layered Structure Ceramic.

Antiferroelectric (AFE) materials have been intensively studied due to their potential uses in energy storage applications and energy conversion. These materials are characterized by double polarization-electric field (P-E) hysteresis loops and nonpolar crystal structures. Unusually, in the present work, Sr1.68La0.32Ta1.68Ti0.32O7 (STLT32), Sr1.64La0.36Ta1.64Ti0.36O7 (STLT36), and Sr1.85Ca0.15Ta2O7 (SCT15), lead-free perovskite layered structure (PLS) materials, are shown to exhibit AFE-like double P-E hysteresis loops despite maintaining a polar crystal structure. The double hysteresis loops are present over wide ranges of electric field and temperature. While neutron diffraction and piezoresponse force microscopy results indicate that the STLT32 system should be ferroelectric at room temperature, the observed AFE-like electrical behavior suggests that the electrical response is dominated by a weakly polar phase with a field-induced transition to a more strongly polar phase. Variable-temperature dielectric measurements suggest the presence of two-phase transitions in STLT32 at ca. 250 and 750 °C. The latter transition is confirmed by thermal analysis and is accompanied by structural changes in the layers, such as in the degree of octahedral tilting and changes in the perovskite block width and interlayer gap, associated with a change from non-centrosymmetric to centrosymmetric structures. The lower-temperature transition is more diffuse in nature but is evidenced by subtle changes in the lattice parameters. The dielectric properties of an STLT32 ceramic at microwave frequencies was measured using a coplanar waveguide transmission line and revealed stable permittivity from 1 kHz up to 20 GHz with low dielectric loss. This work represents the first observation of its kind in a PLS-type material.

One-Shot Synthesis of B/N-Doped Calix[4]arene Exhibiting Narrowband Multiple Resonance Fluorescence.

A novel macrocycle of B/N-doped calix[4]arene (C-BN) was synthesized by a one-shot double boronation. Owing to the structural tension and electron-donating properties of the nitrogen atoms in the macrocycle, reaction selectively proceeds between the adjacent benzene rings outside the macrocycle. C-BN shows a highly centrosymmetric structure with two multiple resonance (MR) fragments bridged by tertiary amine groups at the 1,3 positions of the benzene ring. Benefiting from the large intermolecular distance (>4.6 Å) between adjacent MR-emitting cores, C-BN also exhibits excellent narrowband emitting features against aggregation-induced quenching and spectrum broadening. Optimized organic light-emitting diode devices based on C-BN exhibit high maximum external quantum efficiencies of 24.7-26.6 % and small full width at half maximums of 25-28 nm over a wide doping range of 1-12 wt %.

One‐Shot Synthesis of B/N‐Doped Calix[4]arene Exhibiting Narrowband Multiple Resonance Fluorescence

AbstractA novel macrocycle of B/N‐doped calix[4]arene (C‐BN) was synthesized by a one‐shot double boronation. Owing to the structural tension and electron‐donating properties of the nitrogen atoms in the macrocycle, reaction selectively proceeds between the adjacent benzene rings outside the macrocycle. C‐BN shows a highly centrosymmetric structure with two multiple resonance (MR) fragments bridged by tertiary amine groups at the 1,3 positions of the benzene ring. Benefiting from the large intermolecular distance (>4.6 Å) between adjacent MR‐emitting cores, C‐BN also exhibits excellent narrowband emitting features against aggregation‐induced quenching and spectrum broadening. Optimized organic light‐emitting diode devices based on C‐BN exhibit high maximum external quantum efficiencies of 24.7–26.6 % and small full width at half maximums of 25–28 nm over a wide doping range of 1–12 wt %.

Synthesis and crystal structure of di-μ-methoxo-bis(oxido{N′-[3-(oxidoimino)butan-2-ylidene]benzohydrazonato-κ3 O,N,O′}vanadium(V))

The structure of the dimeric oxomethoxovanadium(V) complex, [V2(CH3O)2(C11H11N3O3)2] or [VO(μ-OMe)(L)]2 (1), with N′-[3-(hydroxyimino)-butan-2-ylidene]benzohydrazide (H2 L, where 2 Hs represent the dissociable oxime and amide protons) is reported. The oximate functionality can coordinate through either the O or the N atom. In the present complex, it is coordinated through the O atom. Here, methoxo groups bridge the two VV centers with a V...V separation of 3.3275 (10) Å. Within the centrosymmetric edge-shared dioctahedral structure, each metal center is in a distorted octahedral NO5 environment, assembled by the O,N,O-donor L 2– ligand, bridging OMe− groups and the oxo group. The complex is diamagnetic in nature and brown in color. Solution electrical conductivity measurements confirmed its electrically non-conducting behavior.

Reorientation of DABCO (1,4-diazabicyclo[2.2.2]octane) in hydrogen-bonded 1:2 molecular complexes DABCO-2(SBA) with substituted benzoic acids SBA

The molecular complexes of DABCO-2(SBA) with substituted benzoic acids SBA, which have the hydrogen-bonded trimeric unit, were prepared to investigate the DABCO reorientation in the trimeric unit. By the analysis of the temperature dependence of 1H NMR spin-lattice relaxation time, the correlation time of the DABCO reorientation was determined as a function of the temperature. It is suggested that a change of potential energy of the reorientation is caused with increasing rate of reorientation resulting in a structure change of the trimeric unit to a centrosymmetric structure. The correlation between the activation energy of the DABCO reorientation and the bond nature of the hydrogen bond involved in the trimeric unit is also discussed.

Hexagonal Lu1-xInxFeO3 Room-Temperature Multiferroic Thin Films.

The hexagonal rare earth ferrites h-RFeO3(R = rare earth element) have been recognized as promising candidates for a room-temperature multiferroic system, and the primary issue for these materials is how to get a stable hexagonal structure since the centrosymmetric orthorhombic structure is generally stable for most RFeO3 at room-temperature, while the hexagonal phase is only stable under some strict conditions. In the present work, h-Lu1-xInxFeO3 (x = 0-1) thin films were prepared on a Nb-SrTiO3 (111) single-crystal substrate by a pulsed laser deposition (PLD) process, and the multiferroic characterization was performed at room temperature. With the combined effects of chemical pressure and epitaxial strain, the stable hexagonal structure was achieved in a wide composition range (x = 0.5-0.7), and the results of XRD (X-ray diffraction) and SAED (selected area electron diffraction) indicate the super-cell match relations between the h-Lu0.3In0.7FeO3 thin film and substrate. The saturated P-E hysteresis loop was obtained at room temperature with a remanent polarization of about 4.3 μC/cm2, and polarization switching was also confirmed by PFM measurement. Furthermore, a strong magnetoelectric coupling with a linear magnetoelectric coefficient of 1.9 V/cm Oe was determined, which was about three orders of magnitude larger than that of h-RFeO3 ceramics. The present results indicate that the h-Lu1-xInxFeO3 thin films are expected to have great application potential for magnetoelectric memory and detection devices.

Nonreciprocal charge transport in topological kagome superconductor CsV3Sb5

Nonreciprocal charge transport phenomena are widely studied in two-dimensional superconductors, which demonstrate unidirectional-anisotropy magnetoresistances as a result of symmetry breaking. Here, we report a strong nonreciprocal transport phenomenon in superconducting CsV3Sb5 thin flakes. The second harmonic voltages, mainly originating from the rectification effect of vortex motion, are unambiguously developed with in-plane and out-of-plane magnetic fields, and their magnitudes are comparable to those in noncentrosymmetric superconductors. The second harmonic magnetoresistances split into several peaks and some of them reverse their signs by ramping the magnetic field or the current within the superconducting transition. The nonreciprocity suggests a strong asymmetry in CsV3Sb5. The centrosymmetric structure and symmetric electronic phases in CsV3Sb5 can hardly induce the distinct nonreciprocal transport phenomenon, which could be correlated to a symmetry breaking from an unconventional superconducting order parameter symmetry.

Hardware Implementation of Euclidean Projection Module Based on Simplified LSA for ADMM Decoding

The Euclidean projection operation is the most complex and time-consuming of the alternating direction method of multipliers (ADMM) decoding algorithms, resulting in a large number of resources when deployed on hardware platforms. We propose a simplified line segment projection algorithm (SLSA) and present the hardware design and the quantization scheme of the SLSA. In simulation results, the proposed SLSA module has a better performance than the original algorithm with the same fixed bitwidths due to the centrosymmetric structure of SLSA. Furthermore, the proposed SLSA module with a simpler structure without hypercube projection can reduce time consuming by up to 72.2% and reduce hardware resource usage by more than 87% compared to other Euclidean projection modules in the experiments.

Decentering the Symmetry via Docking B and F in the KBe2BO3F2-Family Structure.

Deep-ultraviolet (DUV; <200 nm) nonlinear optical crystals arouse a great research interest in modern optical material science as they are key parts of solid-state lasers. Since KBe2BO3F2 (KBBF) still is the only crystal which can generate DUV coherent light practically, exploring other available structures in the DUV region by revising KBBF-family structure templates is necessary. In this paper, two KBBF-family structures are designed by adjusting the directions of BO3 groups or docking B and F atoms in known β-Be2BO3F (BBF). The first BBF structure with a P6322 space group is designed by strictly aligning the BO3 groups of even layers and odd layers in β-BBF. It is very interesting that docking B and F atoms forms novel B-F bonds, which destroy the inversion symmetry of the structure, making the centrosymmetric β-BBF structure with the R3̅c space group convert to a noncentrosymmetric BBF structure having the R3c space group. This noncentrosymmetric BBF structure exhibits a DUV cutoff edge shorter than 150 nm and a second harmonic generation effect comparable to that of KH2PO4 (KDP; d36 = 0.39 pm/V), indicating its feasibility as a frequency-doubling crystal in the DUV region. Our conversion design provides an effective way for uncovering noncentrosymmetric structures in KBBF-family structures.

Dynamic electrical response of vortex polarization in (Pb0.9Sr0.1)TiO3/SrTiO3 artificial superlattice thin films

Artificial superlattice thin films with alternative Pb0.9Sr0.1TiO3 (PST) and SrTiO3 layers were fabricated via pulsed laser deposition. The vortex domains were formed by adjusting the unit cell number of the PST layer to be 20. The electrical response measured by time-resolved synchrotron x-ray diffraction with the repeated pulse voltages of a time interval of 1000 μs indicates that the reorientation of dipole moments in the vortex domains is susceptible to the applied electric field and is a reversible process. Although the centrosymmetric vortex domain structure is not considered to exhibit piezoelectricity, an evident change in the out-of-plane lattice constant with the applied electric field was confirmed. The magnitude of the electromechanical response at 600 kV/cm was estimated to be 19 pm/V, which is nearly comparable to the piezoelectric constant d33 of bulk PbTiO3.